In present state of the art audio coders, perceptual models based on characteristics of a human ear are typically employed to reduce the number of bits required to code a given input audio signal. The perceptual models are based on the fact that a considerable portion of an acoustic signal provided to the human ear is discarded—masked—due to the characteristics of the human hearing process. For example, if a loud sound is presented to the human ear along with a softer sound, the ear will likely hear only the louder sound. Whether the human ear will hear both, the loud and soft sound, depends on the frequency and intensity of each of the signals. As a result, audio coding techniques are able to effectively ignore the softer sound and not assign any bits to its transmission and reproduction under the assumption that a human listener is not capable of hearing the softer sound even if it is faithfully transmitted and reproduced. Therefore, psychoacoustic models for calculating a masking threshold play an essential role in state of the art audio coding. An audio component whose energy is less than the masking threshold is not perceptible and is, therefore, removed by the encoder. For the audible components, the masking threshold determines the acceptable level of quantization noise during the coding process.
However, it is a well-known fact that the psychoacoustic models for calculating a masking threshold in state of the art audio coders are based on simple models of the human auditory system resulting in unacceptable levels of quantization noise or reduced compression. Hence, it is desirable to improve the state of the art audio coding by employing better—more realistic—psychoacoustic models for calculating a masking threshold.
Furthermore, the MPEG-1 Layer 2 audio encoder is widely used in Digital Audio Broadcasting (DAB) and digital receivers based on this standard have been massively manufactured making it impossible to change the decoder in order to improve sound quality. Therefore, enhancing the psychoacoustic model is an option for improving sound quality without requiring a new standard.